On 17/02/12 21:32, nandan amar wrote:
Hello,
I am having two data set original and predicted.
I want to dind QQ-plot fot it.
I tried in following manner :
qq(original~predicted)
and error was :
Error in qq.formula(o ~ p) : y must have exactly 2 levels
There is an option "qtype" which dosent make any difference.
What is the correct way for plotting QQ-plot or am I missing something.
To start with, you are missing telling us that the function qq() is
from the *lattice* package.
Secondly you are missing reading the error message. What
does it *say*? Think about it.
It says that (rather strangely, it seems to me) that the left hand
side of the formula must be a factor with two levels. Obviously
then you must combine your observations into a single vector
and create a factor indicating to which of the two samples each
entry of that vector belongs. Something like:
y <- c(original,predicted)
f <- factor(rep(c("o","p"),c(length(original),length(predicted))))
require(lattice)
print(qq(f ~ y))
Alternatively you could save hassle and use base graphics:
qqplot(original,predicted)
cheers,
Rolf Turner
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